INITIATION OF DEVELOPMENT IN EGG OF ARBACIA. 407 



cortex between fertilizin and sperm guarantees this incorporation. 

 Cell division is thus the end result of fertilization. On this 

 hypothesis, then, the experiments here reported suggest a mode of 

 attacking the fertilization-reaction apart from cell division. 



In the third place, our results suggest the possibility of testing 

 the validity of various theories of fertilization : for example, the 

 oxidation (Loeb), the permeability (R. S. Lillie, McClendon, 

 Gray), and the viscosity (Fischer and Ostwald, Heilbrunn) theo- 

 ries. If, after treating Arbacia eggs with hypertonic sea-water of 

 the strength used in the experiments cited above, we were to find 

 no increase in permeability or oxidation, for example, but on in- 

 seminating these eggs were to find pronounced increase, the case 

 for such increase as the " cause " of fertilization would demand a 

 hearing. But hypertonic sea-water alone of the strength used in 

 our experiments increases the rate of oxidation and permeability. 

 Moreover, this being true, even if there were an additional increase 

 in the rate of oxidation (or permeability) following the insemina- 

 tion of these eggs previously exposed to hypertonic sea-water, and 

 if this increase plus that due to hypertonic sea-water alone were 

 equal to the increase of an equal number of eggs from the same 

 female following normal insemination, we could not hold the oxi- 

 dation (or permeability) theory as proved. For the fact still re- 

 mains that oxidation (or permeability) increase is not inseparably 

 bound up with the fertilization-reaction. 



The case is similar with the viscosity theory of fertilization. 

 Mrs. Andrews long ago showed by means of subjecting eggs to 

 pressure that a rhythm of viscosity changes accompanies the cleav- 

 age process. It may also well be that following the liquefaction 

 of the cortex, as in the egg of Echinarachnius, the ectoplasm gels. 

 Also, Lillie finds that in unfertilized eggs of Chcetopterus in the 

 mesophase of first maturation, though stratification of the endo- 

 plasm readily results from centrifuging, the ectoplasmic layer re- 

 mains unaffected. That fluid substance diffuses from nucleus into 

 cytoplasm is of course well known. This has been shown especi- 

 ally for the egg in the germinal vesicle stage. Says F. R. Lillie 

 on this point : " During this period of diffusion of the fluid sub- 

 stance of the germinal vesicle and the ensuing polarization of the 

 ectoplasm and endoplasm, the protoplasm as a whole possesses a 



